Relay input circuit

ABSTRACT

A relay coil is divided into two series connected sections and a dissipation resistor is connected in series with one lead of both sections to improve the drop out response of the relay. The dissipation resistor is shunted by a transistor the base of which is connected through coupling resistors to the other leads of the coil sections. The transistor operates as a switch to short circuit the dissipation resistor when power is applied to the relay coil to retain the pick up response of the relay. An alternative embodiment has a single coil section and coupling resistor. The dissipation resistor is connected to one lead of the coil section and the coupling resistor connects the transistor base to the other lead.

United States Patent [151 3,666,998 51 May 30, 1972 Wielebski [54] RELAYINPUT CIRCUIT [72] Inventor: Wayne H. Wielebskl, Milwaukee, Wis.

(73] Assignee: Allen-Bradley Company, Milwaukee, Wis.

22 Filed: Feb. 4, 1971 211 App]. No.: 112,530

[52] U.S. Cl. ..317/123, 317/D1G/4, 317/1555, 3l7/D1G. 6

[51] Int. Cl. ..HOlh 47/04 [58] Field of Search... ...317/D1G. 4, DIG.6, 123, 148.5 R,

[56] References Cited UNITED STATES PATENTS 3,582,718 6/1971 Spellman..3l7/148.5 R

3,356,910 12/1967 Bushnell ...3l7/148.5 R

3,172,020 3/1965 Spinelli et a1. ..317/D1G. 6

Primary Examiner-L. T. Hix Assistant Examiner-Ham E. Moose, Jr.Attorney-Arthur H. Seidel and Barry E. Sammons ABSTRACT sistor. Thedissipation resistor is connected to one lead of thecoil section and thecoupling resistor connects the transistor base to the other lead. I

8 Claims, 2 Drawing Figures I Patented May 30, 1972 5 fi I I 1 I a 1 1 I1 1 l 1 i||||||||l||1|1 Tl 4" m W n U M fi 3 9 q 4. W 2 M H w M J n W ww H M M 2 7/0 D H M w m A A m N n N n u H A M M Z m u l l l I l I l I Il I ll r /J I- INVENTOR WAYNE H-WIELEBSK ATTORNEY RELAY INPUT CIRCUITBACKGROUND OF THE INVENTION The field of the invention is input circuitsfor d-c relays connectable to a-c power sources. Prior relay inputcircuits generally contain one relay coil connected to a standardfullwave bridge rectifier comprised of four diodes. When the relay isdeactuated, its drop out response is determined by the rate at whichtheenergy stored in the coils magnetic field is dissipated. The faster thefield collapses, the shorter the response time of the switchescontrolled by the relay. In prior input circuits the relay coil isshunted by the very low resistance path formed by the forward biaseddiodes of the rectifier circuit. To improve the drop out response of therelay therefore, an energy-dissipating device, such as a resistor or azener diode, is commonly added in series with the relay coil. Althoughsuch devices improve the drop outresponse by rapidly dissipatingtheenergy stored in the coils magnetic field, their series connection withthe coil slows the pick up response of the relay. Thus, in an effort toimprove the drop out response of the relay, the elapsed time betweenactuation of the relay and response from the switches is increased. Inprior art input circuits the value of the energy dissipating 'device ischosen by compromising both the pick up and drop out responses. g

'. SUMMARY OF THE INVENTION The relay input circuit of the presentinvention includes an energy dissipating device connected to one lead ofthe relay coil, andan electronic switch connected in shunt relationshipwith the energy dissipation device and having acontrol element connectedto the other lead of the relay coil. The electronic switch is operableto shunt the energy dissipation device when power is applied to therelay coil, and operable to open, or drop out of the circuit, when thepower is removed from the relay coil. v

An inherent characteristic of an inductor is its resistance to thechange in current flow through'it. Thus when the power supplied to therelay coil through the rectifier circuit is disconnected, the coilsmagnetic fi'eld begins to collapse and it begins to generate a current.This is accompanied by a change in the voltage polarity of the relaycoil which is sensed, by the electronic switch. The electronic switchresponds by opening thus injecting the dissipation device into thecircuit to absorb theenergy in the collapsing magnetic field. v

The circuit of the present invention is particularly applicable tosealed contact relays such as that disclosed in my U.S. Pat. No.3,605,049 entitled Sealed Contact Relay where a pair of relay coilsgenerate magnetic flux to operate a plurality of reed switches. Tooperate the reed switches, direct current is supplied to the coils, andtherefore, when operating the relay from an a-c power source, arectifier circuit is included which provides a low resistance path forthe deactuated coils.

A general object of the invention is to improve the drop out response ofa relay by inserting an energy dissipation device in series with therelay coil without slowing the relays pick up response. A transistor isconnected to shunt the energy dissipation device when power is appliedto the relay, and to drop out, or open, when the relay is deactuated.

Another object of the invention is to-provide a means of adjusting thedrop out response of the relay without affecting its pick up response.Because the electronic switch shunts the energy dissipation device whenthe relay is actuated, the impedance of the input circuit to the relaycoil is low regardless of the value of the energy dissipation device.The dissipation device can be a resistorwhich the user can easilyinstall to provide the drop out response he desires.

Still another object of the invention is to provide an inexpensive,compact and reliable circuit for improving the drop out response of arelay.

The foregoing and other objects and advantages of the invention willappear from the following description. In the description reference ismade to the accompanying drawing which forms a hereof, and in whichthere is shown by way of illustration and not of limitation preferredembodiments of the invention. Such embodiments do not represent the fullscope of the invention, but rather the invention may be employed in manydifferent embodiments, and reference is made to the claims herein forinterpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical schematicdiagram of a preferred em- DESCRIPTION OF PREFERRED EMBODIMENTSReferring to FIG. 1, an electrical circuit for a sealed contact relay isdesignated by the dashed line 1. An a-c power source 2 in series with aswitch 3 is connected across input terminals 4 and 5 of the relay 1. Arelay coil divided into a first coil section 6 and a second coil section7 has one lead of the first coil section 6 connected to the inputterminal 4 and its other lead connected through a common point 8 to onelead of the second coil section 7. The other lead of the second coilsection 7 is connected to the input terminal 5. Both coil sections 6 and7 are wound on the magnetic core of the relay such that the fluxesgenerated by them when current flows through them to the common point 8is additive. This is designated in standard fashion in FIG. 1 by thedots adjacent the leads of the coil sections 6 and 7.

One lead of a power dissipation resistor 9 is connected to the commonpoint 8 and its other lead is connected to the anodes of a firstrectifier diode 10 and a second rectifier diode 11. The cathode of thefirst diode 10 is connected to the input terminal 4, and the cathode ofthe second diode 11 is connected to the input terminal 5. They collectorof an NPN of a second switching transistor 12 is connected to the commonpoint 8 v and the dissipation resistor 9. The emitter of the transistor12 is connected to the other lead of the dissipation resistor 9 and theanodes of the diodes l0 and 11. The base of the transistor 12 isconnected to the input terminal 4 through a first coupling resistor 13and to the input terminal 5 through a second coupling resistor 14. g 1

When the switch 3 is closed, positive current, flows altemately intoterminal 4 through the first coil section 6, through the secondrectifier diode l1 and out terminal 5; then into terminal 5, through thesecond coil section 7, through the first rectifier diode 10 and outterminal 4. The pick up response of the relay is determined by theelapsed time between actuation of the switch 3 and a response by the'reed switches controlled by the'magnetic field generated by coils 6 and7. To decrease this time interval, or in other words increase ,the pickup response, the electrical resistance of the two current paths outlinedabove is kept to a minimum.

The switching transistor 12 is an electronic switch which closes toshunt or short out the dissipation resistor 9 when the switch 3 isclosed. As long as power is supplied through the switch 3, base currentflows through either coupling resistor 13 or 14 causing the switchingtransistor 12 to saturate, or turn on. The values of the couplingresistors 13 and 14 are chosen both to protect the switching transistor12 and provide suflicient base current to saturate the transistor 12when power is applied to the relay 1.

When the switch 3 is opened, the magnetic field generated by the coilsections 6 and 7 begins to collapse, generating a current into thecommon point 8. At this point the input terminals 4 and 5 swing negativewith respect to the common point 8 and the base emitter junction of thetransistor 12 becomes reverse biased. The transistor 12 drops out ofsaturation and turns off. The current flowing into the common point 8thus flows through the dissipation resistor 9, to the rectifier diodes10 and 11, and back to the coil sections 6 and 7. The

is rapidly dissipated as heat in the dissipation resistor 9.

Other dissipation devices such as a zener diode can be sub-PNPtransistor can be substituted for the switching transistor 12. v

The embodiment shown in FIG. 2 is an adaptation of the above 'circuit toa single coil relay. Such a relay circuit is designated in H6. 2 by thedashed lines 15. It has two input terminalsl6 and 17 connected to an a-cpower source 18 through aswitch 19. Four rectifier diodes 20 23 areconnected to the input terminals 16 and 17 in a standard full-wavebridge rectifier configuration. The cathodes of the diodes 20 and 2!connect together and to one lead of a dissipation resistorv 24. Theother lead of the resistor 24 connects to one lead of the relay. coil25, the other lead of which is connected to the anodes of the diodes 22and 23 at a common point 26. The emitter of a PNP switching transistor27 is connected to the lead of the dissipation resistor 24 connected tothe diodes 20 and 21, and its collector is connected to the other leadofthe dissipation resistor 24 connected to the relay coil 25. The base ofthe switching transistor 27 is connected to the common point 26 througha coupling resistor 28.

'When the a-c power source 18 is connected to the input termina'ls l6and 17 by closing the switch 19, positive current flows alternativelythrough the diodes 20 and 21 downward through the relay coil 25 andalternately through the diodes 23 and 22. This'current flow holds thevoltage at the common point 26 negative with respect to the voltage onthe emitter of the switching transistor 27. Asa result, thebase emitterjunction of the switching transistor 27 is forward biased and thetransistor 27 is'saturated, or turned on. Thus, when the power issupplied to the relay, the dissipation resistor 24 is effectivelyshunted or short circuited by the switching transistor 27 allowing arapid buildup of current flow through the relay coil 25. When the switch19 is openedthe magnetic field of the relay coil 25 begins to collapseand generate a current through the diodes 20 23. This current flows intwo loops. One through the diodes 20 and 22, and the other throughdiodes 21 and 23. As a result of this collapsing field, the common point26 is driven .positive with respect to the emitter of switchingtransistor 27; This reverse biases the emitter base junction and turnsthe switching transistor 27 off. As a result, the resistor 24 isinserted into the circuit with the relay coil 25, and dissipates theenergy stored in the magnetic field.

As with the circuit in FIG. 1, other devices can be substituted for theresistor 24 and the transistor 27. Additionally, the series connectionof the dissipation resistor 24 and relay coil 25 can be reversedallowing the use of an NPN switching transistor 27 .-ln such anarrangement the coupling resistor 28 is connected to the cathodes of thediodes 20 and 21 rather than common point 26. Other arrangements arepossible if two dissipation resistors and two switching transistors areused. The essential feature of the invention is a series connection ofthe energydissipation device to one lead of the relay coil and shuntingthe dissipation device by an electronic switching device having acontrol element connected to the other lead of the relay coil. Theinvention thus makes use of the polarity change occurring across therelay coil to insert an energy dissipation device into the circuit.

What is claimed is:

1. An input circuit for a direct current relay coil the com device withits control element connected to the other lead of said relay coil,wherein said electronic switch is operable in response to the voltagedrop developed across said relay coil when energizedby saida-c powersource to short circuit said energy dissipation device and responsive tothe polarity reversal in the voltage drop across said relay coil to openwhen the relay coil is deenergized thereby inserting said energydissipation device into the circuit defined by said relay coil and saidrectifier circuit.

2. The input circuit as recited in claim 1, wherein said elec tronicswitch is a transistor with its collector connected to one lead of saiddissipation device and its emitter connected to the other lead of saiddissipation device and its base is the control element.

3. The input circuit as recited in claim 2, wherein a coupling resistoris connected between the transistor base and the other lead of the relay'coil.

4. The input circuit as recited in claim gy dissipation device is aresistor.

5'. An input circuit for a direct current relay coil having'first andsecond coil sections, each section having one lead con- 3, wherein saidenernected to a'common point, the other lead of the-first section beingconnected to a first input terminal and the other lead of the secondsection being connected to a second input terminal, the combinationcomprising:

two rectifiers connected in series second input terminals; an energydissipation device connected between the common point and the connectionpoint of the two rectifiers; and an electronic switch having a controlelement, said-switch connected in shunt relation to. said energydissipation device with its control element connected to the first andsecond input terminals, wherein said electronic switch is operable toshort circuit said energy dissipation device when a power source isapplied to said input terminals and to open when'said power source isremoved from said input terminals. I 6. The input circuit as recited inclaim 5, wherein said electronic switch is a transistor with itscollector and emitter connected to the energy dissipation device and itsbase connected to the input terminals. v

7. The input circuit as recited in claim 6, wherein a first between thefirst and coupling resistor connects the transistor base to the firstinput

1. An input circuit for a direct current relay coil the combinationcomprising: an energy dissipation device having one lead connected toone lead of the relay coil; a full wave bridge rectifier circuit havinga pair of input terminals adapted for connection to an a-c power sourceand a pair of output terminals, one of said output terminals connectedto the other relay coil lead and the other of said output terminalsconnected to the other lead of said energy dissipation device; and anelectronic switch having a control element, said switch connected inshunt relation to said energy dissipation device with its controlelement connected to the other lead of said relay coil, wherein saidelectronic switch is operable in response to the voltage drop developedacross said relay coil when energized by said a-c power source to shortcircuit said energy dissipation device and responsive to the polarityreversal in the voltage drop across said relay coil to open when therelay coil is deenergized thereby inserting said energy dissipationdevice into the circuit defined by said relay coil and said rectifiercircuit.
 2. The input circuit as recited in claim 1, wherein saidelectronic switch is a transistor with its collector connected to onelead of said dissipation device and its emitter connected to the otherlead of said dissipation device and its base is the control element. 3.The input circuit as recited in claim 2, wherein a coupling resistor isconnected between the transistor base and the other lead of the relaycoil.
 4. The input circuit as recited in claim 3, wherein said energydissipation device is a resistor.
 5. An input circuit for a directcurrent relay coil having first and second coil sections, each sectionhaving one lead connected to a common point, the other lead of the firstsection being connected to a first input terminal and the other lead ofthe second section being connected to a second input terminal, thecombination comprising: two rectifiers connected in series between thefirst and second input terminals; an energy dissipation device connectedbetween the common point and the connection point of the two rectifiers;and an electronic switch having a control element, said switch connectedin shunt relation to said energy dissipation device with its controlelement connected to the first and second input terminals, wherein saidelectronic switch is operable to short circuit said energy dissipationdevice when a power source is applied to said input terminals and toopen when said power source is removed from said input terminals.
 6. Theinput circuit as recited in claim 5, wherein said electronic switch is atransistor with its collector and emitter connected to the energydissipation device and its base connected to the input terminals.
 7. Theinput circuit as recited in claim 6, wherein a first coupling resiStorconnects the transistor base to the first input terminal and a secondcoupling resistor connects the transistor base to the second inputterminal.
 8. The input circuit as recited in claim 7, wherein the energydissipation device is a resistor and the rectifiers are diodes.